Distant type~Ia supernovae have been used as calibrated
standard candles out to z=0.8 (\bar{z} ~q 0.55) to
measure the combination ~\Omega\rm M -
\Omega\Lambda using the classical magnitude-redshift
relation. Extending the redshift range will reduce and
eventually break the (\Omega\rm M,\Omega\Lambda)
degeneracy, and also discriminate between a non-zero
cosmological constant and models of hypothetical
intergalactic grey dust. We present here preliminary results
from the most recent very high-redshift (z~1) Type Ia
supernova searches of the Supernova Cosmology Project. The
supernovae were discovered at the CFHT 3.6-m telescope using
the CFH12k camera (run in queue mode), the CTIO 4-m
telescope using the MOSAIC camera and the Subaru 8.2-m
telescope using SuprimeCam. The observations were
coordinated with spectroscopic follow-up at Keck, VLT, and
Subaru. The optical photometric follow-up was obtained at
WIYN, WHT, and TNG for the brighter supernovae, and at HST
for the faintest supernovae. The VLT and Gemini made
possible the near-IR photometric follow up.

This work was supported in part by the NASA Space Telescope
Science Institute.